The present invention refers to a device for localising a transmitter unit.
Today many people have difficulties to know where different things or objects are located, for instance with regard to such things as keys, cellular telephones, bicycles or other vehicles, bags etc. The problem ought to be more significant due to the growing amount of things which we uses daily. The problem does not only concern things or objects but also the difficulty to know the position of domestic animals or other individuals, for instance children.
U.S. Pat. No. 4,954,836 discloses an arrangement for determining the position of a transmitter For the determination of the position, several antennas which are located at different positions are utilized. The antennas are positioned at a large distance from each other.
U.S. Pat. No. 5,513,854 discloses a system for following the position of one or several persons moving on a field, in particular a sports field, and which each carries a micro transmitter. The set of antennas is provided to receive signals from the micro transmitters. The antennas are provided at a large distance from each other.
U.S. Pat. No. 5,021,794 discloses a system for localising persons carrying a micro transmitter. A plurality of mobile receivers is provided to receive a signal from a micro transmitter and for localising the micro transmitter with respect to the direction and the distance.
In these known devices the receiving arrangements have a complicated structure comprising several separate units.
WO97/43660 discloses a device for localising and detecting a microwave source at short distance within an area. The device comprises at least four antennas arranged in two pairs. The phase displacement between the signals to the two antennas in each pair is calculated and by means of the calculated phase displacement the source is localised.
The object of the present invention is to provide improved possibilities to supervise different objects and/or persons.
This object is obtained by the device initially defined, which is characterised in that the base unit comprises at least two antennas, which are positioned at a relatively small distance from each other and which each is arranged to sense said signal, and a processing member which is arranged to calculate at least the direction to said transmitter unit by means of the signals sensed by the antennas. By such a single base unit, the determination of the direction may be made in a simple manner. Since the antennas are provided at a small distance from each other, the base unit may have small dimensions and a compact shape. Consequently, the base unit may be carried by one person. Thanks to the attachment means comprised by the transmitter unit, which preferably has small dimensions, the transmitter unit may be attached to an arbitrary object, a person or an animal, the position of which thus may be supervised.
According to an embodiment of the invention, said signal is sensed by a phase displacement between the different antennas due to said distance between the antennas. Thereby, the processing member may be arranged to measure this phase displacement and to calculate said direction by means of the phase displacement measured. Thereby, a first and a second of three separate antennas may form a first pair of antennas, wherein a first phase displacement of the signal received between these two antennas is determined. and the second and the third of the antennas form a second pair of antennas, wherein a second phase displacement of the signal received between these two antennas is determined, By means of the first and the second phase displacement said direction from each of said pairs may be calculated. It is also possible by means of the first and the second phase displacement to determine at least one approximate position of said transmitter unit.
According to a further embodiment of the invention, said transmitter unit comprises a receiver member and the base unit a transmitter member. Consequently, it is possible to let the base unit be arranged to transmit a signal to said transmitter unit which may be arranged to transmit the signal back to the base unit, wherein the processing member may be arranged to measure the time period from the transmission of the signal to the transmitter unit until the signal is received by the base unit, and by means of the time period measured to determine the distance to said transmitter unit. In such a manner, it is also possible, in addition to the determination of the direction to the transmitter unit, also to obtain a proper knowledge about the distance from the bass unit to the transmitter unit. Advantageously, the processing member may be arranged to Galculate the position of said transmitter unit by means of the determined direction, obtainable by means of one single pair of antennas, and the determined distance, obtainable by means of one or two of the antennas of said single pair.
According to a further embodiment of the invention, the base unit may be arranged to activate the transmitter member of the transmitter unit by a transmission permission which is transferred to the transmitter unit via the transmitter member of the base unit and the receiver member of the transmitter unit. In such a manner. the transmitter member of the transmitter unit may be activated only when its position Is to be determined, which reduces the energy consumption in comparison with if the transmitter member of the transmitter unit would have been continuously activated.
Advantageously, the transmitter member of the, base unit and the receiver member of the transmitter unit may be arranged to transfer said transmission permission by means of a protocol, preferably a CDMA/CD protocol.
According to a further embodiment of the Invention, each of said antennas comprises an essentially straight antenna. Advantageously, the antennas may extend in essentially the same direction. The distance between two adjacent antennas may be less than 1 meter, preferably less than 60 cm and in particular about 30 cm. The resolution of the determination of the position is controlled by the distance between the antennas. Preferably, the antennas may be arranged in a circular configuration which results in a satisfactory spatial resolution.
According to a further embodiment of the invention, the base unit is mobile, either as a portable unit or for instance mounted in or to a vehicle.
According to a further embodiment of the invention, the device comprises at least two transmitter units, wherein each transmitter unit is arranged to transmit a signal according to an identification protocol and wherein the base unit is arranged to identify the transmitter unit in question by means of said identification protocol. In such a manner it is possible for a user to supervise the position of a very large number of objects by only one base unit.
According to a further embodiment of the invention, a display member is arranged to display information about said position of said transmitter unit to a user. The display member may be an integrated part of the base unit or may be formed by a unit, such as a computer or a screen, connected to the base unit.